As a system for remotely controlling vehicle-mounted equipment, an electronic key system is proposed. This system operates to change over the locked state and the unlocked state of vehicle doors based on the result of collating the ID codes accomplished by the bidirectional communication between a portable electronic key (portable device) carried by a vehicle user and a unit mounted on the vehicle. This system resets a steering lock and permits an engine to be started when the user holding the electronic key is inside the vehicle compartment.
The unit mounted in the vehicle of the electronic key system includes an exterior transmitter provided outside the vehicle compartment to transmits a request signal, an interior transmitter provided inside the vehicle compartment to transmit the request signal, a receiver that receives a response signal from the electronic key, and an ECU that controls vehicle-mounted equipment such as doors based on the results transmitted to, and received from, the electronic key. The exterior transmitter and the interior transmitter transmit the request signals maintaining a predetermined electric transmission output power. Therefore, an area for detecting the electronic key is established in a range reached by signals from the exterior transmitter and the interior transmitter. This makes it possible to monitor a user holding the electronic key who approaches the vehicle, who gets in the vehicle or who gets off the vehicle.
For example, if the user holding the electronic key who is going to get in the vehicle approaches the vehicle and enters into the detection area, the electronic key transmits a response signal including an ID code to the vehicle-mounted unit in response to the request signal. When it is determined that a predetermined relationship is satisfied, such as the ID code in the response signal from the electronic key is in agreement with the registered ID code, the vehicle-mounted unit transmits a control signal to a door lock control unit which is vehicle-mounted equipment to place the doors in an unlock standby state. When the user holding the electronic key touches the door handle in this state, the door lock control unit detects it through a touch sensor and unlocks the doors.
When the user holding the electronic key gets in the vehicle causing the electronic key detection area to be shifted into the interior of the compartment from the exterior of the compartment, the vehicle-mounted unit works to control the vehicle-mounted equipment, such as resetting the steering lock and permitting the engine to be started based on the collated result of ID codes.
When the user holding the electronic key gets off the vehicle after having stopped the engine of the vehicle, the electronic key detection area shifts to the exterior of the compartment from the interior of the compartment. In this case, when, for example, a door lock switch provided near the door handle is operated, the vehicle-mounted unit so instructs the door lock control unit as to lock the doors. However, when the electronic key detection area remains interior even if the door lock switch is operated, the vehicle-mounted unit inhibits the door lock control units from locking the doors to prevent the key from being locked interior.
In the above electronic key system, a variety of controls are executed depending upon whether the electronic key detection area is interior or exterior. Therefore, the detection areas of the exterior transmitter and of the interior transmitter must be properly set.
In particular, when the detection area inside the vehicle is narrow and does not cover the entire compartment, it may happen that the electronic key is not detected interior even if the electronic key, in practice, is interior. In this case, it may happen that the steering lock of the vehicle is not reset or the engine is not started. Conversely, when the detection area inside the vehicle is too broad covering even the exterior of the compartment, it may happen that the doors are not locked even if the user holding the electronic key who is off the vehicle to lock the doors.
Therefore an electric current flowing into the antenna of the transmitter may be adjusted by varying the resistance of a current-limiting resistor for each of the models of vehicles in the stage of developing the vehicle. The signal transmission output of the interior transmitter is thus adjusted to obtain a desirable detection area.
Even if the signal transmission output is adjusted for each of the models of vehicles, however, the detection area may often vary depending upon the individual vehicles. The conventional method is not capable of coping with the variation for each of the vehicles.
Further, the expansion of the detection area varies depending upon the electromagnetic wave environment in which the vehicle is placed. The conventional method is not capable of coping with the variation in the expansion of the detection area that is dependent upon the electromagnetic wave environment.